Diabetes mellitus is a prevalent disease that costs the American public over $5 billion/year in invasive testing procedures and $132 billion/year in related healthcare costs. Types I and II diabetes affect an estimated 171 million people in the world today. The disease is generally manifested by disorders in blood levels of insulin, a pancreatic hormone that helps convert glucose into energy. Insulin is necessary for glucose absorption by cells. Unused glucose remains in the blood and is then removed by the kidneys.
Type 1 diabetes, sometimes called insulin-dependent diabetes or juvenile-onset diabetes, results from a shortage of insulin. With Type 1 diabetes the pancreas makes little or no insulin usually because insulin-producing beta cells have been destroyed. Type 1 diabetes usually appears suddenly and most commonly in those under age 30. Type 2 diabetes, also known as noninsulin-dependent diabetes or adult-onset diabetes, usually results from the body's inability to process insulin effectively. With Type 2 diabetes, the pancreas generally makes some insulin. However, the insulin is not effective because of the cell membrane resistance to penetration. About 90 to 95 percent of all people with diabetes have Type 2 diabetes.
Diabetes sufferers must monitor their blood glucose levels regularly to avoid long term complications from hyperglycemia (an overabundance of blood glucose) as well as symptoms of hypoglycemia (a deficiency of blood glucose). Long-term complications from hyperglycemia can damage the eyes, nervous system, kidneys, and cardiovascular and circulatory systems, as well as hinder the body's overall resistance to infections. Cuts and sores may heal more slowly and diabetics are prone to gum problems, urinary tract infections, and mouth infections. Symptoms of hypoglycemia include weakness, dizziness, disorientation, tingling in the hands and feet, and rapid heartbeat.
The proper treatment of diabetes includes maintenance of blood glucose at normal levels, thus frequent monitoring of blood glucose concentration is extremely important in maintaining health and reducing risks from complications. Blood glucose monitoring at this time is generally accomplished by obtaining a droplet of blood for further analysis, usually by a finger prick. This is inconvenient and invasive, usually resulting in infrequent testing. Non-invasive blood glucose monitoring has a high medical and economic value and has attracted an intense interest in the scientific, medical and financial communities. Non-invasive monitoring could dramatically improve disease management and quality of life of stricken individuals through more frequent testing and timely detection of changes in blood glucose level.
Most non-invasive techniques utilize some type of spectral analysis. However, one of the major obstacles in glucose measurement by spectral methods is the interference of the tissue matrix. The water containing tissue in which the glucose measurement needs to be performed has the highest transparency in the wavelength range of 0.8-1 μm. However this is also the range where the glucose spectral signature is relatively weak and thus hard to separate from the matrix. In contrast, in the spectral region where glucose has well defined spectral features (mid-IR) the tissue water absorption is high and therefore the optical path is very short. This coincidence of spectral features makes non-invasive blood glucose monitoring by spectral absorption or emission especially challenging.